Automatic telephone system



May 26, 1925;

'r. e. MARTIN AUTOMATIC TELEPHONE SYSTEM Filed March 15, 1921 TZE I Fatcnted May 26, 1925.

UNITED STATES PATENT OFF ICE.

TALBOT G. MARTIN, OF CHICAGO, ILLINOIS, ASOTGNOR T0 AUTOMATIG ELECTBIO COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

Application filed March 15, 1921. Serial No. 452,468.

To all whom it may. concern:

Be it known that I, TALBOT G. MARTIN, a citizen of the United States ofAmcrica, and a resident of Chicago, CookCounty, and State of Illinois, have invented certain new and useful Improvements in Automatic Telephone Systems, of which the following is a specification.

The present invent-ion relates in general to automatic telephone systems, but more especially to large automatic systems which employ both primary and secondary line switches for the purpose of connecting calling lines with idle first selector switches; and the object of the invention is the provision of various improvements in a system of this kind which tend to increase its utility and commercial success. In particular the invention contemplates the use of secondary line switches of the rotary type, and arrangements are shown whereby such switches may be used to advantage in conjunction with primary line switches of the well known Keith or plungertype. Manyof the features, however, are not limited to this arrangement. V

A special object is the provision of meters and circuits for operating them at appropriate times to record various events 00 curring in the operation of the system WlllCIl it may be desirable to preserve a. record of.

These meters may include a peg countv meter, for registering the total number of" calls outgoing from a primary line switchboard; an all trunkbusy meter, for registering the number of times all. the trunks outgoing "from a primary line switch-board become busy; and a flostcall meter, for registering the number of calls that fail because no outgoing trunks are available.

The foregoing features and others not now specifically mentioned will be described here,

matter with reference to the accompanying drawings, which show sutlieient oil the apparatus in an automatic telephone system to enable the invention to be. explained and understood. v

It should be understood that there are various novel features also described, but not claimed. These features are being claimed in a divisional application,Serial No. 20,855, tiled April (5, 1925.

Referring to the drawing, the reference character A indicates an automatic telephone substation of the ordinary type having the usual talking instrumei'italities and a calling device S for controlling the automatic switches at the exchange. The line conductors 11 and 12 terminate at the eX- change in the individual line switch G, which is a line switch of the wellknown Keith or plunger type, and hence will not need to be described in detail. Briefly stated, the function of the line switch G is to extend the associated line when calling to anidle trunk line. In accordance with the usual practice, the lines entering the exchange are divided into groups, and all of the line switches associated with the lines in each group may be controlled in their trunk selecting operations bya common master switch. The master switch which is associated with the group which includes the line switch C is shown in the lowerleft I hand corner of the sheet and is indicated by the reference character E. This master switch 1s of the well known solenoid type such as is in common use in the automatic I telephone exchanges throughout the country.

Secondary line switches are employed in the 7 present system and accordingly the trunk lines from the primary line switchboards will extend to secondary line switches rather than to first select-or switches; The

arrangement of the trunking between the primary and secondary line switch-boards is well. understood. There may be a plurality of groups oi secondary line switches and each group of primary line switches will have outgoing trunks extending to secondary line switches in each secondary group, so that any calling subscriber will be given access to the trunk lines outgoing'irom all of the secondary groups. In this manner I a large number 01"- first selectors, say one hundred or more, maybe combined in one large group thus securing an increased trunking emciency, The advantages gained by the use of secondary line switches, however, are well known and need not be discussed in detail.

One of the trunk lines outgoing from the primary group which includes the line switch 0 is shown in the drawing, and extends to the secondary line switch I). The line switch D oi the well known rotary type, having" wipers which normally stand. on the trunk line last used, and which move in a "forward direction only. As usually constructed, this line switch has a semi-circular bank comprising twenty-five contact sets and, double wipers standing at an angle of 180 :degrees apart.

The jack J and the lamp L are provided ary line switch group whichincludes the line switch D become .busy, and at other times. It will be convenient howcver,.to go into this later on during-the explanation of the operation. of the system.

Having described the-apparatus, involved briefly, itsv operation will now be-desci'ibed more in detaillwith a, view. to pointing out,

the particular features.ofnovelty disclosed hereim .Eor this purpose itwill be assumed that the subscriber at ,.substation A. desires.

to callsome other subscriber in ,the system,

and the operation. of the primary and. sec;. ondary line SW1tC-l18S,G and Dan connectin i. the line ofsubstat on.Ate a.trunk liiie,eX-.--

tending .to. a firstselec tor.switch.will be described. h'enthe receiver. 1s..reino.*e.d. at

substation Aacircuit is completed over the...

line conductors 11 and 12,1":01 theline relay 16 of the,line switch C. UPOD,ii6ITgiZ]11g.

the line, relay 1.6,...closes acircuit tor thepull down windinglfi of the line switch. at ar1nature 2", .Upon energiz ng, the pull down winding operates, both. the cut-,otf armature 2* and the pluiigei', arin,23, thefl orliier be. ing effective to disconnect the linecondutw tors 11 and 12. from the Ewinding,oit the line relay and from the grounded common conductor 46, respectively; while the latter forces the bank spr ngs 30, 31 32, and 33 into engagement with contact-s34, 35, S6, and 37,.

respectively. By the engagement ofbank springs 30 ;1iid 33 with-contacts 34. and, 31,,

the line conducto"s llnand 12 are extended into connectionwitlrthe trunk line ,conduc-m tors 4:0 and 42, and a circuit is accordingly completed for. the line relay 50 of the sec ondary line switch D. The linorelay 50 is accordinglyenergized and at its armature 53 closes aholdingcircuit for the lineiswitcli C, which may be.traced from ground by.

way of the working contact of arn'iature and the ,said armature, normally closed contact springs controlled by armature 58, release trunk conductor 4:1, contact 35, bank spring .31., and the holding winding lflo t the line switch C to battery. This holding circuit is established, before the slow acting line relay 16 of the line .switch has time to deenergiae and is eft'ective to retain the,

vlun 'eriitin and t e outwit armat r 2% p p v lock the master switch shaft.

inoperated position. .A ground potential 315 also placed on theprivatenorn al conduc-- tor 15 which extends to multiple test contacts on the banks of the connectors which have access to the line. of substation A,

whereby the line is guarded against intrusion in .the. customary manner. Another circuit closed by the operation of the line switch C.iscompletedbythe engagement of bank springs 32 with contact 36. This cuit is thus completed by way. of the master "switch-test wiper 108 and the le:t'thauii winding of the startingrelay 100 to battery.

Relay 100 is-according-lyienergizeduaind at its leit-hand arii'iature completes a circuit ,places a ground on conductor 43 and a Cik well understood, when the locking relay is energized it releases themaster switch shaft (controlling .all the idler linei-switch plunge ,ers) and the shaft instantly :turns in a COUJitOLhQlOCk-WISB. direction-- under control ot a governor, theoperating iforce being supplied a heavy spring under tension.- .The testovipers L08 and 107 are attached to this shaft, ,trom which it-w-ill. appear-thatthese test ,wipers will immediately be moved Ofi-ilOlll their associated tenth test contacts-- :and into. engagement. with tl16"lSSOC1t1tGCl' ninth test. contacts.---Assuminga:that the ninth trunk1liiie is; idle, there will be no ground potential'onithe ninth testcontacts,

the starting relay -l0.0-wil-ldeenergize to open tll31ClTCult.O-f-tll6 locking-relay lol, and thelatter relay WIll ClBGDQTg-LZG to again It may be pointed. out in this connection that w ion the lockingi'elay lOLis energized it. closes acircuit. for the open mainqrelay 103 which disconnectsv the common conductor from thenongroiuided pole ofthe :batteryt. 'This is to prevent theoperation'ot any other line switches while the inasterkswitch shaft isbe ing movedironi one. .trunk to anoth r by .tli.-:.:-

master switch.

Cont nuing nownviththe operation of the secondary line switch D, when the line relay 50. is energized. as. explained.hei;'einbetorc,,. r

it closes a circuitat its armature St-which. includes the. winding of the switching relay.

51. and the winding of the stepping magnet 52 in series, while atithc same tiineby means of, armature.Z55 the test wiper (iiiis. connects vedv to this circuit ata'point midway between the said. relay andthe said. magnet. wlhc operation, 110w depends .upon whether the trunk line with which the line switch wipers Y are associated is busy oridle.,. 11. this trunk l ne is busy there will be a groundpotential on the test; contact engaged by test wiper 66, such as testcontactliQ;tor example, the. .SWltClllIlg' relay 51 will be short circuited,

and-the stepping magnetEQ-being supplied,

with direct ground viathe tcstzwiper will op rate in. the mann r of a buzzer t0 advanre the switch wipers step by step in search of 66 will find no ground potential on the test contact 72, the rotation of the switch will cease and the switching relay 51 being no longer short circuited will energize in series with thestepping magnet 52, the latter remaining inoperative on account of the high resistance of the switching relay. Upon energizing, relay 51 connects the incoming release trunk conductor 41 to the test wiper 66 by means of armature 58, and at armature 57 connects its own lower terminal to the now continuousconductor, extending from the test wiper 66 back over conductor 41 to the line switch C. The line relay 50 being still energized, the test wiper 66 is connected to ground by these operations in order to render the selected trunk line busy. In addition to the foregoing, at armatures 56 and 59 relay 51 disconnects the incoming trunk conductors 1-0 and 42 from the windings of the relay 50 and from ground, respectively, and extends them by way of wiaers and 67 bank contacts 71 and 73 l 3 and conductors 77 and 7 9 to the line relay of the first selector switch in which the selected trunk line terminates. Although this switch is not shown, its operation is well understood and it will be suflicient to state that the line relay of the selector is energized over the circuit of the calling line and closes a circuit for the associated slow acting release relay. The latter relay, upon energizing, places a ground potential upon the release trunk condiictor 78, thereby establishing a holding circuit for the switching relay51 of the secondary line switch D, and for the holding winding 17 of the primary line switch C. This holding circuit, it will be understood, is established before the slow acting line relay 50 has had time to deenergize.

The remainder of the operations in which the calling subscriber controls the first selector taken for use, and a plurality of other automatic switches through the medium of his calling device S, to complete the connection to the desired called line, are well understood and as they have nothing special to do with the present i11\"G11i3lO11,tl10S6 operatious will not be further considered, except to say that when the calling subscriber has finished talking, the restoration of his receiver to the switch-hook causes the automatic switches to restore to normal with the result that ground is disconnected from the release trunk conductor 78. This operation breaks the holding circuit for the primary and secondary line switches G and D and the said switches are restored to normal position, it being understood that the restoring operation. at the secondary line switch D consists merely in the deenergization of the switching relay 51.

Having described the system in a general way, it will be convenientnow to explain the various features which I have incorporated therein with a view to enhancing its commercial success. One of these features is a new arrangement for making all of the trunk lines incoming to a group of secondary line switches busy whenever all of the trunk lines outgoing from such secondary group become busy. It will be appreciated that it is necessary to do this, since if calls were permitted to arriveat a group of secondary line switches when no trunks were available outgoing from such group, it would inevitably happen that such calls would be lost, i. e., they could not be successfully com pleted. In order to accomplish the desired result, and considering the group of secondary line switches which includes the line switch D, a series of chain relays are provided, one for each outgoing trunk, and these chain relays are connected, one toeach of the release trunk conductors. It follows that as fast as the trunk lines become busy the chain relays will be energized, and when all of. the trunk lines are busy all of the chain relays will be energized, with the result that ground is placed on the conductor 82, thus closing an energizing circuit for the relay 83. Uponenergizing, relay 83 closes at armature 89 a circuit for relay85, which upon attracting its armatures connects ground to the conductor 93. The release trunk conductor 41 of the trunk line which terminates in the secondary line switch. D is normally connected to the conductor93, and if the trunk line is not otherwise engaged it is made busy anyway. Relay 85 may be a large multiple contact, or gang relay, or a. number of relays connected in series or parallel may be used; at any rate, at the same time that conductor 93 is grounded similar conductors extending to all of the remainingsecondary line switches in the same group are grounded also, thus making all of the trunk lines incoming to the group in question busy.

As a further result of the energization of relay 83, upon all ofthe trunk lines beconiing busy the conductor 92 is grounded momentarily for the purpose of operating the. master switches in all of the primary groups from which trunk lines lead to the particular secondary group in question. The slow acting relay 84 is normally energized, but when relay 83 attracts its armature the circuit-of relay 84 is broken. Relay 84:, how ever, does not retract its armature immediately and in the meantime relay 83 places ground on conductor 92 by ,means of its armature 88. The grounding of conductor ture 120 and at its armature 121 closes the circuit of the locking relay 101. Upon energizing, relay 101 closes a circuit for the open main relay 103 and at the same time unlocks'the master switch shaft mechanically so'that it is free to move to the left, or in a counter clock-wise direction, under control of the main spring and governor, as previously explained; Since relay 102 has been locked in energized position, this move. ment will continue until the wipers 10! and 108 arrive at the first test contacts in their respective banks at which time the line switch plungers will be opposite the first trunk. The arm 122' now closes contact springs124t and 125, thus completing a cirlocking circuit of relay 102, permitting this relay to fall back, and also closes a new circuit'for' the lockingrela-y 101, in'order that this latter relay may be held up after the relay 102 has deenergized. In addition, relay 104 closes a'cir'cuit for the solenoid 106.

Upon the energization of the solenoid, the

nuisterswitch shaft is rotated by a continuous movement in a clock-wise direction until all of the plungers are lined up opposite the tenth trunk, wipers 107 and 108 being restored to the position shown in the drawing. The arm L3 now disengages spring 126 from the armature of relay 104 and this armature is released to break the circuit of the solenoid 106 and the circuit of relay 101, Relay 101 now deenergiz'es and locks the shaft in position opposite the tenth trunk. There is nothing particularly new in most of these operations at the master switchand they have been described merely in order to make clear the purpose of placing momentary ground on conductor 92 under the circumstances stated. Obviously when the primary master switches are operated, any line switch plungers which happens to be disengaged from the shaft are picked up and are again brought under the control of the inaster switch so that there will be no danger of any of them Another feature is a. provision for making all the incoming trunks at agroup of secondaryline switches busy, and for operating the primary master switches, as described in the'foregomg, 111 case the ma n fuse should blow, which supplies operating battery to the linoswitches of the group. Consideringthis feature alittle further, the

reference character 96 indicates the main fuse which supplies operating current to all of the secondary line switches which are associated with'the line switch D in the same group' It will be understood, of course, that in practice relay 50 and the stepping magnet 52, instead of being connected direct to the ungrounded pole of the battery, are connected thereto by way of the fuse 96, as are the relays 83 and 84. Now, if this fuse should blow for any reason all of the secondary line switches in the group will at once becomeinoperative, and it will clearly become'necessary to render all the incoming trunk lines busy, and also to operate all the primary master switchesin order to pick up any line switch plungers which may happen to be standing on trunk lines extending to the secondary group in question. This is accomplished as follows: lVhen the fuse blows, relay Set will deenergize and by means of its armaturesf86 and 90 circuits are closed simultaneously for energizing relay 85, and for placing a ground on conductor 92. Relay 85 is energized, grounding conductor 93 and similar conductors in order to make the incoming trunk lines busy, while at armature 91 this relay removes ground from conductor 92. Conductor 92 is thus grounded momentarily, as in the case previously explained, and by the consequent locking up of relay 102 and similar relays associated with the other, primary master switches all of these master switches are ope 'ated as and for the purpose already set forth. I

The keys I and K together with a plurality of other similar keys, may be located on a test panel in some convenient place in the switch room, and are provided for the purpose of enabling an attendant, or switchboard man, to locate trouble on the common conductor 200 and its various branches. There may be as high as half a dozen groups of secondary line switches, and twenty-five or more groups of primary line switches, from which it will be clear that there may be six branches corresponding to branches 92 and 93, and twenty-live or more branches corresponding to the branch 94, and it will be appreciated that if any one of these branches should become permanently grounded in some way, the consequences would be extremely serious. The test keys are provided, therefore, to enable the attendant to quickly locate such trouble if it should occur, which is accomplished by operating the keys successively and observing the sound of the buzzer 95. As soon as any particular key is operated, thebranch associated with such key is disconnected the connnon conductor will still have a ground on it and the buzzer will operate, indicating to the attendant that the trouble has not yet been located. Obviously if the keys are operated in quick succession a few seconds only will be required to locate the particular branch which isin trouble.

The key K is known as an emergency pick up key, and may be mounted on the test panel with the keys just described. It

is useful to the attendant for trying the operation of the primary master switches, and may also be used in case the regular circuits for automaticallyoperating these master switches should get out of order. The exchange is always equipped with various supervisory signals and alarms which indicate the blowing of fuses, or the busy condition of trunk groups, etc. The attendant is thus, at all times, aware of the condition of the equipment and in case some of the automatic devices fail to perform their functions he may accomplish the desired results by means of the emergency key.

As stated herein before, a number of meters are provided for recording certain events occurring during the operation of the system, and these meters and their functions will now be explained/ The peg count meter M will be considered first. It will be observed that the common conductor 44, which supplies battery to the pull in windings 'of'all the primary line switches of the group which includes the line switch C, includes the winding of the low resistance relay 112, and it will be clear, therefore, that whenever one of these line switchesis operated relay 112 will be operatedalso. Each time relay 112 operates it closes a circuit for the meter'M and this meter, there fore, will register the total number of calls outgoing from the group in question. 7

The meter M is the all trunk busy meter, which functions as follows: In case all of the trunks outgoing from the primary line switch group are busy all of the test contacts in the bank associated with test wiper 107 will be grounded, and the starting relay 100 will remain energized as long as this condition continues. hen relay 100 isenergized it closes a circuit for the locking relay 101 in order to initiate the operation of the master switch, as explained before, and it also closes a parallel circuit through the relaylll. This latterrelay is a special relay construeted as shown in the pending application of John Erickson, Serial #34t8,548, filed December 31, 1919.

lVhen its armature is attracted a circuit is completed for meter MT, but at the same tune a pendulum s set in motion which in vibrating rapidly interrupts the circuit of the'said meter and thus for a certain definite time prevents it from operating. A V relay of this typeis used so that m the ord1- nary operation of the system the meter M will not be caused to register even though relay 111 is momentarily energized from time to time. The time interval of the pendulum controlled by relay 111 is of such duration that the master switch can operate in two complete cycles, and thus the meter will not be operated during the ordinary operation of the master switch in stepping from trunk to trunk,;or even when the master switch moves the plungers from the first to the tenth trunk, while if all the trunks are busy and the master switch is. in continuous operation, the meter will be caused to register.

The remaining meter M is provided for registering calls which fail because no outgoing trunks are available. It will be observed that the common conductor 46, to which the lower side of each subscribers line is connected normally, extends through thewinding of relay 110 to ground. Relay 110, however, is normally short circuited at the armature of the starting relay 100, and it follows, therefore, that in the ordinary operation the system when a subscriber removes his receiver and operates his, line relay, such as the line relay 16, relay 110 will not be energized. In case all the trunks are busy, howeverthe starting, relay 100 will be held up continuously and relay 110 will not be short circuited. Under these circumstances, ifanother subscriber should attempt to make a call, when he removes his receiverrelay 110 willbe energized. This relay is of very high resistance and prevents the line relay of the calling line from pulling up atthis time. Upon energizing, relay 110- closes a circuit for the relay-109, which is a relayfequipped with a pendulum device the same as relay 111. If the start ing relay 100 does not deenergize before the expiration of a definite time interval, relay 109 will permanently close the circuit of the meter M in an obvious manner and the said meter will be caused to register.

' hen the circuits are connected, as shown in the drawing, if the starting, relay falls back before meter M has operated in the case just described, relay 110 will immediately be shortcircuited again and it will fall back to breakthe circuit of relay 109 which in turn will restore its armature and prevent the meter M from being operated, as explained in the preceding paragraph; but if the jumper containing terminals 130 llU and 181 is cut the operation will be different.

, the lamps, such as the lamp L at the wire in the appended claims.

chiefs, or complaint operators desk, are preferably inserted in their acks and when the relay 110 operates in response to a call, during time when all the trunks are busy, it will open the short circuit around its winding and its upper armature so that it will not be restored until the calling subscriber replaces the receiver, even though in the meanwhile one or more of the outgoing trunk hnes should become idle. At the same time, relay 110 closes a circuit for the lamp L and thus notifies the wire chief that some and will tall: to the subscriber and advise him to try the number over again after few minutes. Relay 110 it may be men? lVith this arrangement of the wiring" ister the number of times'all of said trunk lines are busy for-a predetermined time interval.

5. In atelephone system, a group of subscribers line-s, agroup of trunk lines,individual line switches for" ex'tendingcalling subscribers lin'esto idle trunk line's, "a master switch itorcontrolling said line switches in thesele'ction or idletrunk lines, a meter, and means in saidmaster switch responsive to an all trunk 'bu'sy condition for operating said meter. v i

V '6. In a telephone system, a groupvo'f subscribers"lines, ajgrotip'oit trunk lines, individual linefswitches forextending calling subscribers"lines to idle trunk lines, a master switch foifcontrolling said line switches tioned is made slow to energize by provid ing it with a copper slug on its arn'iature end. Thls is done so that it someone should attempt to call during a momentary energization ot'the starting relay 100, while the master switch is stepping from trunk to trunk, the relay 110 will not energize and will not'become locked up under these circonsider to be new and desire to have pro tected by Letters Patent will be pointed out What I claim as my invention is:

1. In a telephone system, a group of subscribers 1ines,a group of trunk lines, individual line switches for extending callmg subscribers lines to idle trunk lines, a meter,

and circuit means responsive to the initia tion of a callfor operating said meter to register the total number of such calls.

2. In a telephone system, a group of subscribers lines, a group of trunk lines, individual line switches for extending calling subscribers lines'to idle trunk lines, a mas ter switch forcontrolling said lineswitches in the selection of idle trunk lines, a meter, and means in said master switch for operating said meter toregister the tO'ttlllllllll'lbGl of calls originating in the group of subscribers lines. y Y

3. In a telephone system, a group of subscribers lines, a group or trunk lines, indi vidual line switches for extending calling subscribers lines to idle trunk lines,"a mas-' ter switch for controlling said line switches in the selection of: idle trunk lines, a battery,

a common operating conductor for said line in theselection of idle trunli'lines, a magnet, meansflin said master switehfor energizing said magnet when all or said trunks become bi'isy," a meter, and mechanism controlled by said magnet when the same is energized for operating said mete'r after a predetermined time interval, i i

p 7. In a telephone system, a group of subscribers lines, a group e f trunk lines, individual line switches for e2;te1iding calling subscribers lines to idle trunk lines, a meter, and circuit means responsive to the initiation" of a call while alltrunks are busy for operating said meter to register the number 01 calls whichjfail because all of said trunk lines are'biisy.

8. In a telephone system, a group of subscribers lines, a'groupo'ttrunk lines,- individual lin-eswitches forextending calling subscribers lines to idleftrunk lines, means -for preventing the operation of any line switch it all of said trunks are busy, a meter,

a relay,'circuit',connections for operating with said conductor for o )eratim said meter said relay in case a line should attempt to call'while all of 'saidtrunks are busy, and

a meter controlled by said relay;

1 10. In' a telephone system, a group of subscribers" lines, group" of trunk lines, individual line. switches fol-extending calling subscribers lines to idle trunk lines, a relay, circuit connections for operating said relay in case a line should attempt to call while all of said trunks are busy, a met-er, and

mechanism controlled bysaidrelay for p:

crating said meter after a predetermined tnne mter'val.

a n'1eter,.1neans for operatinga plurality of said line switches over their associated lines to seize a plurality of said trunk lines, and means responsive to an all busy condition of said trunks for operating said meter after a predetermined interval of time.

13. In a telephone system, lines terminating' in auton'iat'ic non-directive line switches, trunk lines accessible to said. line switches, a'meter, means for operating a plurality of said line switches over their associated lines to seize a plurality of said trunk lines, means operative when all of said trunk lines are busy for operating said meter, and meansoperative if one of said trunks becomes idle within a predetermined time for preventing the operation of said meter and for pern'iitting the seizure of the non-busy trunk.

let. In a telephone system, calling lines terminating in line switches, trunks acces sible to said line switches, a meter, means operative when a trunk is seized for making the same inaccessible to other line switches, and means responsive to the initiation of another call at a time when'all of said trunks are inaccessible for closing an operating circuit for said meter.

15. In a telephone system, lines terminating in line switches, a master switch for n'mintaining said switches positioned before idle trunk lines, means for making all off said trunk lines busy, a meter, means opcrative when all said trunks become busy for preventing the operation of any of said line switc es, and means responsive when another of said switches is seized for causing the operation of said meter;

16. In a telephone system, lines terminating in line switches, a master switch for maintaining said switches positioned before idle trunk lines, means for making all of said trunk lines busy, a meter, means operative when all said trunks become busy for preventing the operation of any of said line switches, means responsive when another of said switches is seized for causing the operation of said meter, and means for pre venting; the operation of said meter in case a trunk becomes idle within a predetermined time.

11. In a telephone system, lines terminat- .717. In a telephone system, lines terminating in line switches having plungers, trunk lines accessible to said line switches, a master switch for maintaining theplungers of idle. switches b-etore idle trunk lines, means for operating a plurality of said line switches over their associated lines to seize a plurality of said trunk lines, and means responsive to an all busy condition of trunlts for operating said meter.

18,111 telephone system, a group of subscribers lines, a groi'ip of trunk lines, indisaid vidual line switches for extending walling subscribers lines to idle trunk ]ines,a meter, and means responsive to the seizure of the last idle trunk in said group for operating the meter after a predetermined time interval.

19. In a telephone system, a group of subscribers lines, a group oftrunk lines, indt vidual line switches for extending calling subscribers lines to idle trunk lines, a meter, and n'ieans responsive to an all trunk busy condition for a certain predetermined time for operating the meter.

20. In a telephone system, a group of subscribers lines, a group of trunk lines accessible thereto, means for selecting an idle one of said trunks, and a device responsive to the initiation of a call for operating" a meter it there are no idle trunks available for a predetermined time.

21. In a telephone system, a group of subscribers lines, a group of trunk lines, individual line switches for extending calling subscribers lines to idle trunk lines, means for preventing the operation of any, line switch it all of said trunks are busy, a meter, and means responsive to the initiation of a call from aline while its associated line switch is rendered inoperative for operating said meter.

22. In a telephone system, a group of subscribers lines, a group of trunk lines, individual line switches for extending calling subscribers lines toidle trunk lines, two meters, means responsive to the seizure of the last idle trunk of said group for operating one of the meters, and means responsive" to the initiation'ot' a call while all the trunks are busy for operating the other meter.

23. In a telephone system, a group of subscribers lines, a group of trunk lines, individual line switches for extending calling subscribers lines, a master switch for controlling said line switches in the selection of idle trunks, a meter, means responsive to the initiation of a call for operating said meter, another meter, means responsive to an all trunk busy condition for operating said second meter, a third meter, and means for operating it if another call is initiated during an all trunk busy condition.

2 1.- In. a telephone system, subscribers lines, a group of trunk lines, a group of secondary line switches having access to said connection.

ondary line switchesihavingi acoessto said 7 trunk lines 'priinarry line switches having trunk I lines, primary line switches having-accesst0-said secondary line switeheganeans access to said secondaryline switches, means whereby culling subscribers can operate whereby-L1- calling subscriber-cam operate his their primary line switches andu:plurality primary line switch and one of said second--01? said secondaryiline switches to connect my line switches to connect with an idle one with idle trunk lines menns for busy g all cf saiditrunk lines, inennsiOr busy-ingalh-thtlunk l'inesin seid'group,and-means for .the trunk lines of saidlgroupya meter, and counting the number of calls thatare lost means for-operating said meterin case said dUHPtO l' fiS l gmle b y trunk lines are made busy before the secwhile soineof saidsecondary line switches ondary line switch in use has completed the t ng' 111165- In witness whereof,'I-hereuuto si'lhscrihe 25. I11 a telephone system, subscribers my mmwthls 1st W a' hnes, a group of trunk lines, a group of secl TALBOT. G."l\fIARTIN. 

